Chromate-sulfite redox-initiated aqueous polymerization of vinyl chloride



Patented Jan. 12, 1954 CHROMATIC-SULFITE REDOX INITIATED AQUEOUS POLYMERIZATION OF VINYL CHLQRIDE George J. Koch, Jr., laincsville, Ohio, assignor to Diamond Alkali Company, Cleveland, Ohio, a

corporation of Delaware No Drawing. Application November 31], 1950, Serial No. 198,496

10 Claims.

This invention relates to a method for polymervinyl chloride, and more particularly relates to a method incorporating a non-peroxidic redox system for init ating and catalyzing the polymerization of vinyl chloride.

It has heretofore been proposed to polymerize vinyl chloride dispersed in an aqueous medium and, moreover, it has been proposed broadly to catalyze the polymerization of vinyl chloride dispersed in aqueous media by means of an inorganic, non-peroxidic redox system. This broad proposal, however, has been found to be grossly inadequate, and inaccurate in specific instances, in present ng any basis for the use of non-peroxidio oxidizing agents in redox systems for the catalysis of the polymerization of vinyl derivatives. Also, this broad proposal has failed to teach anything relative to the potent al effectiveness and the advantages of employing chromate salts in combination with sulfite salts for this purpose. Indeed, the literature in presenting reaction mechanisms for the reduction of the chromate ion in dilute solution would lead one skilled in the art to the conclusion that the combination of a chromate salt and a sulfite salt would not induce the polymerization of vinyl chloride.

Contrary to the theories presented in the literature referred to above relative to the reaction mechanism for the reduction of the chromate ion,

it has now been found that a redox system composed of sulfite ions as the reducing agent and chromate ions as the oxidizing agent may be caused to react in a dilute aqueous solution in contact with vinyl chromide monomer in such manner as to initiate and catalyze the polymerization reaction to the end that high rates of conversion of monomeric vinyl chloride to polymers having relatively high molecular weight are obtained.

One of the objects of the present invention is to A provide a redox system for catalyzing the polymerization of vinyl chloride, in which system a non-peroxidio oxidizing agent is employed.

Another object of the invention is to provide a method for the redox-catalyzed polymerization of vinyl chloride, in which the redox system is composed of sulflte ions and chromate ions.

These and other objects of the invention will be apparent to those skilled in the art from the disclosure hereinbelow.

I r sent invention is directed to a method of polymerizing vinyl chloride which includes the steps of dispersing monomeric vinyl chloride in an aqueous medium containing a redox system composed of sulfite ions and chromate ions, and recovering a polymerizate from said medium,

In practicing the method of the present invention, the redox system composed of sulfite ions and chromate ions as a catalyst for the polymerization of vinyl chloride may be employed by combining water, a suitable emulsifier or dispersant, if desired, and the redovs stem ingredients, and immediately after or concurrently with the introduction of the redox system ingredients into the aqueous med um, dispersing monomeric vinyl chloride as a liquid in the aqueous medium, and carrying out the polymerization under the autogeneous pressure of the components of the polymerization reaction mass.

Another manner in which the redox system of the present invention may be employed includes combining the water, a suitable emulsifier or dispersant, if desired, and either member of the redox system, dispersing liquid monomeric vinyl chloride in the aqueous medium, and then introducing the other member of the redox system into the aqueous medium, and carrying out the polymerization reaction under the autogeneous pressure generated by the components of the polymerization reaction mass.

Two variations of this latter procedure for carrying the present invention into effect may also be employed to advantage; that is, (1) the liquid monomeric vinyl chloride and the member of the redox system not already present in the aqueous medium may be emulsified or dispersed in the aqueous medium concurrently and gradually over an extended period of time, or (2) the aqueous medium, including an emulsifier or dispersant, if desired, and either member or" the redox system may be frozen to a solid. mass and thereafter liquid monomeric vinyl chloride, together with the remaining member of the redox system, brought into contact with the frozen mass, followed by thawing and agitation of the polymerization mass. It will be observed in either of the latter two procedures, the redox system ingredients and the monomeric vinyl chloride are brought into reactive contact with one another gradually over a period of time, and it is beli ved that such technique is beneficial in promoting high rates of conversion of monomer to polymers having molecular weights of the order of 100,009.

Conditions which have been found to exert an influence upon the polymerization conversion rate in the method of the present invention include temperature, pH of the aqueous medium, the rela-- tive molar proportions of the components of the redox system, the relative proportion of the sum of the mols of the components of the redox system to the mols of monomer employed, and the e proportion of the aqueous medium to the of monomer used.

In practicing the method of the present inventicn, it has been found that the polymerization reaction temperature may suitably be substantially within the range of 25-50 0., preferably, however, Within the range of about 35- l5 C. In general, at temperatures below 25 C. the conversion rate of monomer to polymers is relatively low and results in polymers having molecular Weights in excess of 150,000, which polymers are not technically as desirable as polymers of molecular weights of the order of 100,000, which are more easily compounded. Also, polymerization reaction. temperatures above 50 C. result in the obtaining of very low molecular weight polymers at a very hig conversion rate, which low molecular weight pol mers are generally not as desirable in the synthetic plastics arts as the higher molecular weight polymers obtained with n the preferred temperature range noted hereinabove, in that such low molecular Weight polymers lack the desired degree of tenacity necessary to the fabrication of shaped articles.

The pH of the aqueous medium is preferably maintained substantially within the range of 2-9 during the polymerization reaction, it having been found that where the pH values of the aqueous medium are substantially within the range of 4.5 to 7, the highest conversion rates to polymers having molecular weights of the order of 100,000 are obtained. It is the vinyl chloride polymers having molecular weights of this general order which are technically most useful in the commer cial arts.

The molecular weight values referred to hereinabove, as well as in the discussion following and the specific examples hereinbelow, are calculated from the viscosity of a solution of 1 gram of polymerizate in 100 mls. of solvent cycloheX- anone), as determined by means of a modified Ostwald viscosimeter tube immersed in a constant temperature bath.

The redox system of the present invention is composed of sources of sulfite ions and chromate ble than the alkali metal and. ammonium salts, as

well as the heavy metal chromates and sulfites whose solubility although quite low is determinable.

The preferred sources of chromate ions for the purposes of the present invention include the watersoluble alkali metal and ammonium chromates or bichromates, such as the lithium, sodium, potassium, rubidium, and cesium chromates or hichroroates, as well as chromic anhydride (CrOs). Similarly, the alkali metal and ammonium sul tes. bisulfites, or the metabisulfites, such the lith um, sodium, potassium. rubidium, and cesium sulfite. bisulfite, or metabisulfite, salts are p eferred herein.

Without intending to be lim ted by theoretical cons derat ons as to the natural laws underlying th inv ntion. the obser at ons and discuss ons iven h re n el w are o=ered in re ard hereto as p inci les upon which to base a fea ible process for the polymerization of vinyl chloride by ions. In the neutral or the of the pH range, the

HCrOI ion is believed to predominate in the mixture, Whereas the definitely alkaline portion of the pH range is believed to promote the predominance of the slightly acid portion ion. An analogous condition may obtain in the ionization of sulfite, bisulfite, or metabisuliite salts, in acid solution to give in the equilibrium mixtures both sulfite and bisulnte ions. It is, therefore, the intention here to include these species, as well as others which may result from the various ranges of conditions within which the invention may be employed, under the general term of chromate and sulfite ions.

Whether only one or both of these ionic forms of hexavalent chromium referred to hereinabove are involved in the formation or" sulfite or bisulfite radicals in the aqueous medium, or Whether these ions are capable of becoming radicals ther selves, is not known. It has been found, however, that polymers obtained by initiating and catalyzing the polymerization reaction with redcx systems composed of chromate ions and sulfite ions, exhibit a slight bluish-green coloration, characteristic of trivalent chromium, which coloration is not removed by water washing of the polymer particles, but is removed b washing the polymer particles with oxidizing agents capable of oxidizing trivalent chromium to hexavalent chromium. Moreover, the washings in such case exhibit a slight yellow coloration characteristic of hexavalent chromium. It is believed, therefore, that the trivalent chromium is in some way chemically bound to terminal sulfonic groups in a salt complex, which sulfonic groups originate in the polymer from the reaction of sulfite or bisulfite radicals with the monomer molecules at the initiation of the polymerization reaction.

The redox system composed of sulfite ions and chromate ions employed in the method of the present invention is preferably prepared from chromate and sulfite salts in molar'ratios of chromate ions to sulfite ions, substantially within the range of 1:1 to 1:8. The choice of proportions within this range has been found to be influenced to some extent by the pH of the aqueous medium, it having been found that at pH values above 8, ratios of chromate ions to sulfite ions of the order of 1:1 to 1:3, generally are more eifective in producing high conversion rates than ratios greater in the proportion of the sulfite component. This has been found also at pH values below about 4.5. At pl-I values of about 1.5 and below about 8, ra-

tics of chromate ions to sulfite ions substantially within the ran e of 1:3 to 1:6 have been found to be most eifective in producing high conversion rates of monomer to polymer.

The proportion which the sum of the mols of chromate ions and sulfite ions in the redox system bears to the mole of monomer employed may suitably be within the range oi 0.1+5 mol percent of the monomer; preferably, however, this pro portion is substantially within the range-oi 0.4-1 mol percent for obtaining high conversion rates of monomer to polymer. 1

The proportion of monomer tothe aqueous medium may be substantially within the range of 1:2 to 1:4, but is preferably, however, of the order of about 1:3 for ease in separating and recovering the polymerizate from the aqueous medium.

A suitable emulsifier or dispersing agent substantially inert to the chromate andsulflte ions may also be employed in the aqueous phase in concentrations within the range of 0.5-2.7 of the weight of the monomer, depending upon the emulsifying agent or dispersing agent used and its efficiency in producing. the desired, degree of emulsification or dispersion in neutral, acid. or alkaline media. Emuls-iz'iers which have been found suitable in this. connection include anion active wetting agents, such as the alkyl sulfates, alkyl sulionates, alkyl aryl sulionates. cation action wetting agents, such as quaternary ammonium compounds, and the like, as well as nonionic emulsifying agents, such as the poly-hydroxy compounds, for example, polyvinyl alcohol, ethylene oxide polymers, hydroxy esters and ethers, such as the polyglycols, and the like. However, the alkyl sulfates having from 12 to 14 carbon atoms in the alkyl chain are preferred for the reason that such alkyl sulfates emulsifiersv are readily available commercially in a relatively high state of purity. The purity of the emulsifier is of significance in any emulsion polymerization system since it has long been known that where such emulsifier contains substantial amounts of olefinic alkyl chains, particularly the conjugated olefinic alkyl chains, or where the alkyl chain bears tertiary hydrogen, either of which may be present in certain of the alkyl aryl sulfonates, such compounds are responsible for terminating the polymerization of the above-noted olefinic monomers relatively early in the polymerization reaction period, whereby a low yield of poly merizate results.

The pH of the aqueous medium may be adjusted to the desired point within the above-noted range, with acids or alkalies not of an oxidizing or reducing character, at any step prior to adding the second component of the redox system thereto. In general, it has been found that the pH of the aqueous medium increases slightly as the polymerization reaction proceeds, and although it is not necessary in the practice of the method of the present invention, bufier salts may be added to the aqueous phase in amounts sufficient to maintain the reaction mediumsubstantially constant at a desired point in the abovepH range during the polymerization reaction. Buffers which have, been found suitable for the purposes herein include mixtures of acetic acid and sodium acetate, as well as the universal buffer of Britton and Robinson (Hydrogen Ions, Britton, second edition, page 225) consisting of acetic acid-phosphoric acid-boric acid-NaOH, and the like.

In order that those skilled in the art may bet! ter understand the method of the present invention and in what manner the same maybe carried into. effect, the, following specific examples are ofiered:

Example I Batches composed of 300 parts of water con-. taining 0.93 part of NazSOa and 1 part of a commercial sodium lauryl sulfate purified to. remove sodium sulfate and polymerization inhibitors, are adjusted to, the pH values given in the table below by means of dilute sulfuric acid (10%) and dilute NaQI-I, solutions. The solutions are then frozen at 25 C. in suitable vessels. To the solid masses in each of the vessels there are added 0.14 part of Na2Cr2O7.2HzO dissolved in parts of water and. 100 parts of liquid vinyl chloride monomer. The vessels are closed to the atmosphere, immersed in a constant temperature bath at 40 (3., and the contents of the vessels agitated. The polymerization reaction is carried out at the autogenous pressure of the system. The results are given in the table below:

Redox system pH Redox Time Per- M01. molar hours cent wt.

- gif ggj Nags 0; Init. Final Xw Temperature of polymerization 40 Weight ratio of polymerization medium to monomer=3:1.

Example II Batches composed of 300 parts of water containing 0.93 part of NazSOs and 1 part of commercial sodium lauryl sulfate purified to remove sodium sulfate and polymerization inhibitors are each. gradually combined with 100 parts of liquid monomeric vinyl chloride and 0.37 part of over a period of about five minutes with agita-' tion and at the autogenous pressure of system. The pH values of the several batches are adjusted with dilute sulfuric acid solution 10%), and with dilute NaOH solution (5%) prior to adding monomer and the bichromate salt.

Redox system 2%}? p11, Time, Percent ratio mit. hours conv. NazCl'eOm 2H2 O N51280:;

0. 37 0. 93 1 :3 O. 25 0. 37 0.93 1:3 1. 5 32 0. 37 0. 93 1:3 3. 75 33 0. 37 0. 93 1:3 0. 75 40 0. 37 0. 93 1 3 1 48 0. 37 0. 93 1:3 1. 5 04 0.37 0.93 1:3 0. 75 47 0. 37 0. 93 1 :3 1 57 0. 37 0.93 1:3 1. 5 72 0. 37 0. 93 1:3 0. T5 54 0. 37 0. 93 1 3 1 70 0. 37 0. 93 1:3 1. 3 0.37 0.93 1:3 1. i 87 0. 37 0. 93 1:3 2. (i 95 0.37 0.93 1:3 1. 25 89 0. 37 0. 03 1:3 2. (i 90 0. 37 0.93 1:3 0. 5 25 0.37 0. 93 1:3 1 35 0.37 0.93 1:3 1st 11 0.37 0.93 1:3 2. 6i 12 0. 37 093 1:3 4 17 Redox system, mol percent of monomer=0.6l. Weight ratio of polymerization medium to n10nomer=3 :l. Temperature of polymerization medium=40 G.

Example III Solutions of both C10 and NazSOs are, added to amixture of 300 parts of water and 1 part of purified sodium. lauryl sulfate as described in Example I. The mixture is refrigerated. at -25 C. to a solid mass. One hundred parts of vinyl chloride are added thereafter as a liquid, the whole reaction mass heated to 40 0., with agitation, and polymerization carried out at the 2. The method of claim 1 in which the molar ratio of said chromate ions to sulfite ions in said redox system is substantially within the range of 1:8 to 1:1.

fls s p e of the system. 3. The method of claim 2 in which the sum 7 e of the mols of said chromate ions and said sul- Redoxsystem Redox Time Perfite ions of said redox system is substantially I 4 hours g; within the range of 0.1 to 5 mol percent of said Grog Naiso Fmal monomeric vinyl chloride.

4. The method of claim 1 in which the pH of (0.08317 incl 0087 1 1161 1:2 6 the aqueous medium is maintained substantially 23 4 within the range of 29 during the polymeriza- 'tion reaction. Redox system: 0.59 mol percent of monomer. 5. The method of polymerizing Vinyl chloride Example IV which includes the steps of dispersing monomeric Sodium sulfite is dissolved in 190 parts of water vinyl chloride i n aqueous m di m incontaining 1 part or" purified sodium lauryl sula redox t y t System composed of chrofate, the pZ-i adjusted to 4.4, the mixture reirigmate ions and sulfite ions, and an emulsifier erated at 25 (3., parts of liquid vinyl chlo- 20 effective to emulsify said vinyl chloride in said ride monomer and an aqueous solution of CrOs medium, maintaining the pH of said medium subare then mixed therewith and the whole reaction tantjally Within t range of 2.9 during t mass heated t0 45 C,, with agitation t0 disperse polymerization reaction and recovering a, inyl the monomer. The polymerization reaction is chloride polymer f o said medium carried out at the autogenous pressure of the 5 The method of claim 5 in which the molar System ratio of said chromate ions to sulfite ions in said redox system is substantially within the range of 'Redflsystem Redox PH m Pei: M61. 1:1 to 1:8. Grog Nazsoa i In Final hours 35; '7. The method of claim 6 in which the sum of the mols of sa1d chromate ion and the mols of 037 465 1:1 M 375 L5 81 mos said suliite ion in said redox system is substan- (0.0037 (0.0037 tially wlthin the range of 0.1 to 5 mol percent 385 M5 91 of said monomeric vinyl chloride.

8. The method of polymerizing vinyl chloride For purposes of comparison, certain of the data which includesflle steps of @ntacting an aqueous from the foregoing examples are incorporated medlum contammg catalystlc amounts of a with other data of experiments which are carried ter'soluble salt 0f the class consisting of out in the manner described in Examples 1, II, mates and Sulfites W monomeric yl ch10- and IV above. The data are tabulated below: ride and catalystic amounts of the salt of said Redox system pH o o 2H0 N so 95%; oriii 1 1561 31 01. 3 o i 0 d gi Init' Final s03 monomer While there have been described various emclass which is absent from said aqueous medium, bodiments of the invention, the methods described agitating the resulting mixture under autogenous are not intended to be understood as limiting the a pressure during the polymerization reaction pescope of the invention as it is realized that 69 riod, and recovering a vinyl chloride polymer changes there-within are possible and it is furfrom said medium. 7 V ther intended that each element recited in any 9, The method of polymerizing Viny1 Chbride of the following claims is to be understood as which includes the steps f contacting a fr en referring is an equivalent elements for accom' aqueous medium, a water-soluble salt of the class plishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle be utilized.

What is claimed is:

1. The method of polymerizing vinyl chloride which includes the steps of dispersing monomeric vinyl chloride in an aqueous medium containing a redox catalyst system composed of chromate ions and sulfite ions, and recovering a vinyl chloride polymer from said medium.

consisting of chromates and sulfites with monomeric vinyl chloride and the salt of said class which is absent from said frozen aqueous medium, agitating and. heating the resulting mixture to a temperature substantially within the range of 25-50 C. under autogenous pressure, and recovering a vinyl chloride polymer from said mixture.

10. The method of polymerizing vinyl chloride which includes the steps of dispersing monomeric class which is absent from said medium, agitating r and heating the entire mass to a temperature substantially within the range of 2550 C. under autogenous pressure, and recovering a. vinyl chloride polymer form said medium.

GEORGE J. KOCH, JR.

References Cited in the file of this patent Number UNITED STATES PATENTS Name Date Frey Oct. 20, 1942 Sully Feb. 21, 1950 Crouch Nov. 28, 1950 

1. THE METHOD OF POLYMERIZING VINYL CHLORIDE WHICH INCLUDES THE STEPS OF DISPERSING MONOMERIC VINYL CHLORIDE IN AN AQUEOUS MEDIUM CONTAINING A REDOX CATALYST SYSTEM COMPOSED OF CHROMATE IONS AND SULFITE IONS, AND RECOVERING A VINYL CHLORIDE POLYMER FROM SAID MEDIUM. 